The New Time Travelers: A Journey to the Frontiers of Physics by David Toomey (Norton, £15.99)

There's no such thing as a free lunch - unless it's a time-machine jinn, in which case you can have as many as you want, but you mustn't eat them. A time-machine jinn is a theoretical beast created out of nothing by a consistent time-travel loop. Do this: assemble certain materials at a factory, hook it up to a powerful computer and run away. Instantly an old and battered automatic spacecraft will land, having voyaged for millions of years to find suitable wormholes to use as a time machine, and then used them to hop back to the present, where it downloads its design into the computer to make sure it was built in the first place.

Sounds like science fiction? Actually, it was worked out by physicists. As Toomey's superbly written popularisation shows, the idea of time travel, once not "serious", has attracted increasing scientific attention since it was shown that nothing in Einstein's equations prevents it. Here you will see weird behaviours of time-travelling billiard balls, etchings by Escher, and the "many-worlds" interpretation of quantum mechanics, which also implies a way to think about time: all possible futures exist, as a multitude of universes. So the question of free will is finessed: "Each universe within the multiverse is deterministic, but I exercise free will by moving among them." Which universe would you like to live in tomorrow?

Perhaps not one where "something enormous is approaching fast along a dimension we cannot see", which sounds terrifying, but that's how the physicist authors of this work think things actually are. Think about the Big Bang: why did it happen? Where did it come from? Unlike some physicists, they think these are actually good (and embarrassing) questions, and instead theorise a "cyclic" universe, which lives on a massive "brane" (as in membrane) close to another brane. Periodically these branes collide, and then bounce away again. What we think of as the Big Bang was just one of these regular collisions: the mother of all car crashes, that will happen again, and again.

As the Steinhardt and Turok note, this sounds eerily similar to aspects of Hinduism (which, as they show, contains surprisingly accurate guesses at meaningful cosmic periods). Of course, this theory doesn't solve the origin question completely but merely pushes it back. (An alternative answer comes at the end of Toomey's book: according to physicist J Richard Gott, the universe itself could be a jinn, having created itself by means of a time machine.) Still, they argue persuasively for the elegance of their idea, which makes certain predictions about gravity waves that we might one day be able to detect with a probe. Place your bets.

Four Laws that Drive the Universe by Peter Atkins (Oxford, £9.99)

Among which is to be found the law explaining why my desk gets messier, which is a relief. (I cannae change the laws of physics, captain.) This is a brief and invigoratingly limpid guide to the laws of thermodynamics, such as the conservation of energy or the increase of entropy. The author amiably breaks down and makes mysterious what we took for granted - what, after all, is temperature? - before building it up again, evoking in the reader's mind the pleasure of a puzzle snapping together. I liked Atkins's watchfulness for "slipperiness" of language, as well as the pithiness of his own. "Work is motion against an opposing force." You're telling me.